Some computer systems maintain one or more copies of data so data can be restored after a data loss event. Backups or copies of data are useful for restoring a computer to an operating state after a disaster or restoring a file after it is deleted or corrupted.
Data storage requirements can be considerable since a backup system contains at least one copy of all data. The processes of managing backup operations and organizing storage are complex, time consuming, and in some instances costly.
In an effort to make backup operations more efficient, some backup systems only copy files and directories that have changed since the last backup. In other words, if a file has not changed since the last backup, it is not copied again since a backup version of the file already exists. At the same time, if a file is marked as having a change, then the entire filed is copied again during the next backup operation.
In traditional backup systems, files and directories are marked as being changed even though the data itself did not change. For example, if a user views a file, moves a file to a new directory, renames a file, or changes an access control list (ACL) attribute, then the file is marked as being changed. During a subsequent backup operation, the entire file is recopied even though the content of the file did not change.
Backup systems that copy every file marked as being changed are inefficient since processing resources, time, and ultimately money are unnecessarily spent to recopy data that did not actually change.